1. Field of the Invention
The present invention relates generally to signal processing circuits such as measuring circuits, and more particularly to a compensating apparatus and method for collectively compensating for variations in characteristics of such signal processing circuits caused by a variety of factors. The present invention is also directed to a collectively-compensating-type signal processing circuit provided with such a compensating apparatus.
2. Prior Art
Conventionally, when a measuring device is to be used, warm-up time is provided for the device prior to measurements, during which the measuring device is placed in an operable environment such that circuits within the measuring device has reached a thermally balanced state. For example, devices such as a standard signal generator, spectrum analyzer, power meter, TV level meter, and so on, require a warm-up time of at least 30 minutes or more, normally one hour. Particularly, with electronic circuits arranged within devices associated with high frequencies, since they must be designed to exhibit a low impedance, electric power consumed by respective parts correspondingly becomes large. Some of such devices require a warm-up time of not less than two hours.
Also, a conventional measuring device is externally provided with correction tables (e.g., a correction table for correcting erroneous indications caused by varying temperatures or frequencies) for correcting errors due to variations which cannot be compensated for within the circuits of the measuring device, i.e., variations which cannot be attended to by existing circuit techniques. Thus, the user refers to such correction tables to find a corrected indication value in the table corresponding to an output value indicated by the device.
Conventional signal processing apparatuses including measuring devices as described above, thus, has a drawback that they require long warm-up time and therefore cannot be used immediately after power on. Also, the long warm-up time makes a battery less suitable for powering the device. The measuring device using external correction tables renders the measurement inconvenient and complicated. Further, it is difficult, or expensive even if possible, to compensate for complicated short- or long-term variations occurring in conventional signal processing circuits through the use of conventional circuit techniques.